Reference

NBS

PubliNATL INST. OF STAND & TECH

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*^EAU O* *s NBS TECHNICAL NOTE 1056

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

•QC

100

.U5753

No. 105

1933
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities 2 — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering2 — Manufacturing

Engineering — Building Technology — Fire Research — Chemical Engineering2

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection,

acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234.

2 Some divisions within the center are located at Boulder, CO 80303.
/VSS Techntc^i Nok.

taauM*

<s?c

Picosecond Time Difference .'Ss-7^^

Measurements Utilizing CAMAC-Based Vco./^s

ANSI/IEEE-488 Data Acquisition m3

Hardware

Operating Manual IE3

Version 1.0

D.J. Glaze

S.R. Stein

Time and Frequency Division

National Measurement Laboratory

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

/ V %

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued August 1 983
National Bureau of Standards Technical Note 1056

Natl. Bur. Stand. (U.S.), Tech. Note 1056, 36 pages (August 1983)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1983

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402

Price $3.75

(Add 25 percent for other than U.S. mailing)
CONTENTS

1. Introduction 1

2. Theory 2

3. Hardware Description and Configuration 2

3.1 Crate Configuration 3

3.2 Module Configuration and Installation 3

3.3 System Synthesizer 4

3.4 System Signals, Cables, and Connections 4

3.5 Cables for 5 MHz Signals 4

3.6 Other Cable Connections 6

3.7 Configuration of Remaining Switches 6

3.8 System Controller 7

3.9 System Clock 7

3.10 System Plotter 7

4. Operation 7

4.1 Power Up Sequence 7

4.2 Operation 8

5. Software Description and Discussion 10

5.1 Introduction 10

5.2 Command Structure 10

5.3 General Program Flow for Data Acquisition 11

5.4 Detailed Program Flow for Data Acquisition 12

5.5 Detailed Program Flow for Data Processing 15

Appendix 24

l] l

Picosecond Tine Difference Measurements

Utilizing CAMAC-Based ANSI/ TEEE-488 Data Acquisition Hardware

Operating Manual TE3 Version 1.0

D. J. Glaze and S. R. Stein

Time and Frequency 'Division

National Bureau of Standards

Boulder, Colorado 80303

Automated time-difference measurements at the picosecond level

have been achieved. The system described combines the best properties

of three common methods: the single heterodvne measurement technique,

the frequency divider, and the dual-mixer time-difference measurement

system. This particular system combines two instrumentation standards,

ANSI/IEEE-583 and ANSI/ I EEE-488 with new, modular dual -mixer timedifference measurement hardware. The modular, standardized hardware

together with the new measurement techniques permit the data acquisition modules to be contained in a standard CAMAC crate. This system,

along with an external controller, is capable of measuring eight clocks,

at the present time, and is expandable to twenty-four clocks with

modified software and additional measurement modules. The system noise

-12 -1

performance is described by a (t) = 3 x 10 t for time difference

measurements.

Key words: ANSI/IEEE-488; ANSI/IEEE-583; automated data acquisition

system; dual-mixer measurements; picosecond time-difference measurements

1. Introduction

The measurement system described was developed to make simple, reliable

picosecond time-difference measurements on high-performance atomic frequency

standards utilized in such applications as atomic scale systems, laboratory or

field calibrations, sigma-tau and phase stability measurements. Utilization

of adjacent time-difference or phase points provides frequency measurement

capability. Software and hardware available yield phase data, sigma-tau data

and phase plots (on suitable output devices).

The hardware utilizes two special modules commercially manufactured to

NBS specifications. Other special modules, low-noise, isolation amplifiers,

were not commercially available in the form required at the time the system

was implemented. These items were designed and constructed at the NBS
laboratories. All other items, CAMAC crate and interface modules, clock

timer, and computing calculator operating over the IEEE-488 bus, are

commercially available.

The system has been designed to provide time-difference capability for

measurement intervals of 1 second and longer. The speed of the specific

implementation described below is limited by software to intervals 5 seconds

and longer. Hardware limitations for the present system are due to the tape

cartridge which limits data collection to 100 points each for eight clocks

under test. System performance is best described by a specification of:

o (t) = 3 x 10" 12/t

2. Theory

A theoretical description of the system operation is included in Appendix

1.

3. Hardware Description and Configuration

The modular design of the data acquisition hardware used in this system

employs a standard CAMAC (IEEE-583) crate, Model 1500-P1K, and power supply as

supplied by the manufacturer . The interface modules are designated in the

following way:

Model 3981-Z1B Auxiliary rate controller

Model 3953-Z1B Auxiliary controller adapter

Model 3388-G1A IEEE-488 interface

Equivalent hardware manufactured by other vendors is expected to function

in precisely the same manner but has not been tested.

The following manuals are provided by the manufacturer of the CAMAC

equipment
Model 1500 powered CAMAC crate

Model 3388-G1A IEEE-488 interface

Model 3953-Z1B Auxiliary controller adapter

Model 3981-Z1B Auxiliary crate controller

Model 8021 3981-Based IEEE-488 crate

Controller system

Model 6120-B10 Software manual

Routines for 488-controlled

CAMAC I/O

Block diagrams for the operation and control of the pulse distribution

module and the quad clock measurement modules are also included. These

circuit diagrams are important to an understanding of the system. They

contain sufficient information to permit the design of compatible measurement

equipment.

3.1 Crate Configuration

As supplied , the crate is Model 1500-P1Z. Power to the crate and

modules is derived from a rear mounted, modular power supply. It provides

± 24V dC, ± 12V dC, and ± 6V dC. When mounting the power supply to the crate,

follow instructions provided in the crate manual. Install the sheet

insulating film provided between the power supply and the crate dataway

wirewrap pins. Failure to do so may cause shorts on various pins and destroy

the crate and power supply.

3.2 Module Configuration and Installation

Modules are installed in the following way. The crate is constructed so

that modules are installed from the front into numbered openings or slots.

These slots are numbered from left to right beginning with 1 and continuing

through 25. Slot 25 is not a normal slot, but is used for controllers only.
Connect the 40 pin ribbon cable to the connectors on the back and top of

the 3953 module and the 3981 module. Note that the 40 pin cable does not

connect to the 3388 module.

2 Install the pulse distribution module in the slots labelled 1 and 2.

N=2 for this module.

2

Install the first quad measurement module" in the slots labelled 3 and 4,

and the second one in slots 5 and 6. The crate addresses for these modules

are N=3 and N=5 respectively. Two of these modules will permit measurement of

8 clocks. Up to four more quad measurement modules may be added to the system

allowing measurement of 24 clocks; however software modifications would be

required for these additional modules.

3.3 System Synthesizer

The synthesizer, is offset in frequency by 10Hz below the nominal 5.0 MHz

value. The synthesizer (user provided) must be referenced to the clock which

drives the master channel.

3.4 System Signals, Cables, and Connections

All RF signals are nominally IV rms at the 50 ohm impedance level. With

the present release of system software, (IE3 version 1.0) channel 1 must be

the master channel

.

3.5 Cables for 5 MHz Signals

Connect cables from clocks to be measured, through suitable isolation

amplifiers, to the SMA clock inputs of each quad measurement module. Signals

for the NBS isolation amplifiers should be IV rms at the 50 ohm impedance

level

.

Attach cables from the synthesizer output, again suitably isolated, to

the offset reference SMA connector(s) of the quad measurement module(s).
Install the 3953-Z1R auxiliary controller adapter in the last pair of

slots: 24 and 25. The crate address for this nodule is N=25.

Prior to installation of the 3388-G1A module, set the eight-section

switch on the circuit board so that all sections are off. Install the

3388-G1A in the next pair of slots: 22 and 23. The crate address for this

module is N=23. However, commands written to this module by the program use

the address 700.

Prior to installation of the 3981-Z1B module check to see if the

following wire-wrap jumpers have been installed. If not, install them and

check to see that no shorts exist between wirewrap pins and adjacent traces of

the circuit board. Use only one set of jumpers corresponding to the

particular prom supplied. The circuit board jumper pins are numbered from 1

to 14.

Prom 2708 or Prom TI2716

Connect Pins: 9 to 13 9 to 3

11 to 3 11 to 8

10 to 13 10 to 2

12 to 2 12 to 8

7 to 8 7 to 13

14 to 5 14 to 6

1 to 4 1 to 5

Consult the 3981-Z1B hardware manual on page 4-2. Note the location and

orientation of the prom sockets and install the prom in socket designated prom

1. The four-section switch on the module circuit board should be set so that

all sections are off.

Install the 3981-Z1B auxiliary crate controller in slot 21. N=21 for

this module.
Connect a cable from the isolated signal driving channel 1 to the synthesizer

reference input. The frequency of the reference signal for the synthesizer

should be nominally 5.0 MHz within manufacturers specifications. Set the

synthesizer frequency to 4.9999900 MHz (10 Hz below nominal 5.0 MHz).

3.6 Other Cable Connections

In subsequent discussions the following conventions apply:

QMM = Quad measurement module

PDM = Pulse distribution module

Attach cables as follows. Use LEMO COAX cables:

From To

PDM (Slots 1, 2) QMM(l) (Slots 3, 4)

Master CH 10 Hz in Channel 1 10 Hz out

PDM 10 MHz out QMM(l) 10 MHz in

PDM 10 MHz out QMM(2) (Slots 5, 6)

10 MHz in

PDM ARM/Start out QMM1 ARM/Start in

PDM ARM/Start out QMM2 ARM/Start in

3981 Request 3981 Grant in

Attach IEEE-488 cables as follows:

From To

9825A, 9872A 3388 IEEE-488 Conn.

59308A (see H and I and J below)

3.7 Configuration of Remaining Switches

3981 module. Set halt-cont switch to center position. This switch is

spring loaded and will remain in this position. Set the enable-disable switch

to enable position.

3953 module. Set the online-offline switch to online position. C-Z

switch should be at center position (spring loaded and will return to center).
3.8 System Controller

3 The system controller for this application is a 9825A desk top

calculator. Required components are:

9872A plotter-gen I/O ROM

98216A extended I/O ROM

98210A string-adv prog ROM

As operated in this system, the 9825A has a total of 23228 bytes of

memory. Any other IEEE-488 compatible controller will work with modifications

in software. There may be some effect on system speed.

3.9 System Clock

3

The system "clock" is a 59308A timing generator.

Switch Positions: Front Panel: Function SW: Pacer

Rear Panel: Ext Freq Std: 5 MHz

Ext. Std. Signal: 5.0 MHz derived from

System ref. signal driving channel 1.

Bus Pacer: Off

Trigger and option sections: Not used

Switch A: Al=l; All other sections = zero

3.10 System Plotter

3 The plotting hardware for the system is a four color pen plotter, Model

9872A.

4. Operation

4.1 Power Up Sequence

When all cables and components are properly installed, the crate may be

turned on. Check the multifunction meter monitoring system and the crate
manual to be certain that operating voltages and currents are proper. The

voltages should be at the monitor set point in all cases.

The other IEEE-488 devices may be powered up. The tape cartridge

containing the operating software should be installed in the 98?5A. (Rewind

the cartridge before it is removed. Failure to do so may destroy program or

data stored near the position of the tape head) rewind the cartridge. Press

erase a, then reset, for power-up mode only.

4.2 Operation

Data are stored on the tape cartridge on track 1. This track must be

formatted before the program can store data. One should use the following

commands to format the data tape:

Rewind

TRK 1 Execute

MRK, 800, 64

Execute

Rewind

One may mark more files than 800, but usually only approximately 80? files may

be marked before end of tape (EOT) and an error are encountered.

To begin the data acquisition phase of the operation, one must execute

the following commands:

TRK

Execute

LDF

Execute

Run

The controller will now prompt responses from the operator. The

questions and responses will be described in a subsequent section. After all
entries are made the program will run according to the parameters supplied by

the operator. At the end of the first measurement interval (length specified

by the operator), the 9825A will print out some data and begin the second

measurement interval. Data will be printed or not as the operator specified,

and data points will be recorded on the magnetic tape cartridge. This

continues until at the end of the run, the 9825A will print out some data on

the paper tape and display "Stop. . .operation complete". At this point the

operator should rewind the tape then enter the following sequence:

TRK

Execute

LDF 1 Execute

Run

Now the system will process the data taken in the previous operation and

will again ask the operator questions. After entering all answers to the

questions the program will begin processing the data on the tape cartridge.

The program has various stop points to permit the operator to set up the paper

for plotting and to specify other outputs that may be required. After data

from all clocks have been processed, the 9825A will display "Stop. . .Operation

Complete". At this time the operator may choose to stop or to take more data.

If more data are to be taken, the program on TRK 0, file must be loaded

again. Subsequently, the processing program on TRK 0, file 1 must be loaded

to handle the data processing. Note that the tape is rewound by the data

acquisition task. Data written on the tape by the acquisition are typically

written over the data taken from a previous run. In response to the question

"Begin w tape file No.?', one usually types the numeral 1, followed by

pressing the continue key. The numeral 1 denotes to the operator the first

data file on the tape. The operator may begin a second run at File N + 1,
thereby not writing over the first points taken in an earlier run. One must

remember, however, where the break points are; otherwise, the data processing

task may run together points from more than one set of data, and incorrect

results will occur. One may of course use a second data tape if previous data

are to be retained. The total number of points recorded may not exceed 800 on

any given tape (typically 100 per clock for 8 clocks).

5. Software Description and Discussion

5.1 Introduction

Commands to the data acquisition hardware are typically sent via write

statements from the program in the 9825 which employ ASCII strings.

5.2 Command Structure

An ASCII command is composed of three parts:

Function Code: Choice Of: "F0" through "F31"

Subaddress: Location Choice Of: "A0" through A15"

within the module

Station or Slot No: Choice Of: "Nl" through "N31"

However only slots 1 through 25 are used in this system.

A command sent with the above components will address a particular module

and location within a module. However, no action will be taken unless an

execute command is included and unless the command is written to a specific

address (device) on the bus. A typical command might be:

(First set A$ = "F25A0N2E") Notice that the execute

command (E) is embedded in the string A$.

WRT 700, A$

This command writes, with execute, the string A$ to the bus address 700.

In this software, 700 is the address of the controller in the crate. The

10
string sent, F25A0N2E, causes the crate controller to initiate a measurement

sequence: (This occurs when the above command string is sent to the Pulse

Distribution module through the crate controller.)

F25 is the Measurement command

AO is the Address within the slot

N2 is the Slot no. of the Pulse Distribution module

(701 is the address of the system clock)

(705 is the address of the system plotter)

5.3 General Program Flow for Data Acquisition

As described in Section 5.2, a command has been sent to the 3388 module ,

which then causes a measurement sequence in the PDM module, in Slot N=2, to be

initiated. All measurements are started by the PDM. After the read command

(as above) is received by the PDM, the following sequence occurs:

1. The PDM issues an ARM/Start Command wich arms the counters.

2. The next 10 Hz zero-crossing starts the system counters for all quad

meas. modules.

3. The following 5 MHz zero-crossings, obtained from each of the

individual clock signals, stop the 10 Mhz counters on each individual channel.

At this point the data, in the counters at the time of the measurement,

are stored in registers in the 3981 module. Data are read out in the form of

three bytes (24 bits are required to contain the data word):

1. High order data byte: Bits 24 through 17

2. Middle order byte: Bits 16 through 9

3. Low order data byte: Bits 8 through 1

These three bytes are transferred out of the registers in the 3981 into

variables defined in the 9825A data acquisition task. These variables are

combined algebraically to form the raw data. Both the 10 Hz and 10 MHz

11
counter readings are taken this way, for each clock. Some computations are

performed to calculate the value of the clock phase using the following

equation from appendix 1:

*

2 (tM

) - *!(t

M

) = 2 (N -M )ir + 2(N - M).ir - 2 ^^B 2

(

M

;t

N )]T

c

P

The initial phase reading which was taken during the first interval is

subtracted. The difference, called delta time, is recorded along with the.

channel number, on the magnetic tape cartridge, for each clock measured.

During the time of these calculations and recording, the next measurement

interval is progressing. After the recording on tape is finished, the 9825A

continually checks the counter reading in the system clock, 59308A. When the

counter reaches th$ appropriate value, the software jumps to the initiation of

the next measurement sequence. This process continues until the required

number of points has been taken. The measurement then ends, and the number of

points, the timing interval in seconds, the date and time entered, and the

data label, are printed on the paper tape. The operator then decides whether

to process the data with another program, or to take more data.

5.4 Detailed Program Flow for Data Acquisition

The program tape is placed in the 9825A and the acquisition program TRK

0, File is loaded. After the run command is issued, the program asks if one

wishes to edit the identification file for the clocks:

"Edit Clk Id File?"

The operator may respond with a "n" or any answer except "y" , in which

case the channels will be identified for the print-out in the following way:

For Channel 1: "Chan 1"

For Channel 2: "Chan 2"

etc

For Channel 8: "Chan 8"

12
The operator may also respond with a "y" , in which case the program will

ask: "Channel 1 Clk ID?... 6 Char max". To this the operator should respond

by typing some suitable name for the clock driving channel 1, then press

continue. The program will ask for identification for each clock in turn, and

then the following sequence occurs.

1. Initialize command is sent to the crate, i.e., "ZE".

2. Enable channel operation command is sent to all even sub-addresses of

the two QMM's, i.e., "F26A0N3E".

3. Reset LAM Status command is sent to all odd sub-addresses of the

QMM's, i.e., "F10A1N3E".

4. Reset 10 Hz register overflow command is sent to all even

sub-addresses of the QMM's, i.e., "F9A0N3E".

5. Reset 10 Hz register command is sent to all even sub-addresses of the

QMM's, i.e., "F12A0N3E".

After this sequence is completed, the program asks several questions.

6. "Enter Date. . .dd-mmm-yy" ; the operator types e.g., 27-Apr-82, and

then presses continue.

7. "Label?" The operator may enter a label describing the experiment,

up to 35 characters, then press continue.

8. "Print Data Output?" A "y" answer here causes flag 2 to be cleared.

This in turn causes all data from each point to be printed on the paper tape.

The data are always recorded on the magnetic tape cartridge. If, after a few

points are printed, the operator wishes to stop the print-out, one simply

types "sTg2", followed by "execute", from the live keyboard during a time when

the program is in the timing interval between points. This action will

suppress all further print-outs until the program ends. Any answer other than

"y" to question 8, will inhibit all print out except the value subtracted from

13
the delta time reading during the first timing interval. Selecting the print

option slows the program significantly. With printing, eight clocks require

at least 40 seconds. Without printing, this is reduced to approximately 5

seconds.

9. "Enter Seconds in timing interval". This is the number of seconds

desired for the elapsed time between points. Type the number (not less than 5

discussed above), then press continue.

10. "Number of clocks?" A number from 1 to 8 should be typed, then

press continue. If a number greater than 8 is entered, the program displays

"Max Clocks = 8" and returns to question 10 for the proper response.

11. "No. of points?" The operator should enter the number of points per

clock desired for that run, then press continue. The program must take one

more point in order to compute frequency for the first interval. However,

this is accounted for in the program, and the number of points requested will

be taken, provided there is room on the magnetic tape.

12. "Begin w/tape file no.?" If the first data file on the tape is to

be used, enter 1, and then press continue. If one wants to skip over data

already recorded, e.g., to the 16th point, type 16, then continue. This

option is included only to permit one to save previously recorded data. One

must, however, keep track of these points on the data tape, because the phase

points will not be continuous from one run to the next, the processing program

will not know that more than one run exists in the data set, and erroneous

results will occur.

13. "To start timing, press continue". Here is a pause so that the

operator may start the run on a particular second. When continue is pressed,

the program begins data acquisition according to the entries made by the

operator. The system will run until the specified number of points has been

14
taken, (or until there is no more space on the data cartridge. 100 points

maximum for 8 clocks may be taken).

After the program completes its run, the following items are printed on

the data tape:

"No. of Points=" (e.g.) "100"

"Timing Interval="(e.g. )" 60"

"Date"

"Time" time entered at start of run

"Label" entered at the beginning of run

Now the operator must decide to stop, process the data on the magnetic

tape, or acquire more date.

5.5 Detailed Program Flow for Data Processing

The program from TRK 0, file 1 is loaded into the 9825A as described

above. The system plotter should be set up by entering PI and P2 from the

plotter keys. This matches the plotting window to the size of the paper to be

used by the operator. The plotter select code and address are 705. Then

press run. The program asks several questions.

1. "Edit clock ID files?" The default clock Id's for all eight channels

are: Channel 1, Channel 2,... etc. If the operator wishes to insert other

names for clocks he may enter "y" in response to this question. Then the

9825A prompts for the Id's for all clocks. One may assign 6 characters

maximum for each clock Id. After each Id entered, press continue.

2. "Enter Date: dd-mm-yy" This is an obvious entry, e.g.: 27-APR-82

then press continue.

3. "Label?" Here the operator may enter a description of the data to be

processed. Up to 35 characters may be entered, then press continue.

15
4. "Process data tape?" If one answers "n" or any answer other than

"y", the program branches unconditionally to the end and stops, displaying:

"Stop. . .operation complete". If one answers "y" » tape processing begins with

question 5.

5. "Read all 8 clocks?" A "y" answer here sets a counter so that data

for all 8 clocks will be read from the tape. Branch to question 7. Any other

answer causes a branch to question 6.

6. "Enter No. of Clocks to be Read". Here one enters a number from 1 to

8. The clocks will be read beginnning with clock 1 and ending with the clock

number entered by the operator. The program continues with question 7.

7. "Number of First data point?" Enter the number of the data point

with which the run began. If it is the first point taken, enter 1, and press

continue. If one wants to skip to the 10th point, enter 10, ...etc., then

continue.

8. "Number of last data point?" If 100 points were taken, type 100,

then press continue. If one wishes to process only a partial set of the data,

type the number of the end point and then press continue. One must specify at

least 4 points, otherwise some of the subroutines will not work correctly.

Obviously there must be at least 4 points on the tape from the acquisition

task.

9. "Measurement Interval, Seconds." Here one should enter the number of

seconds in the timing or measurement interval for the data run, e.g., type

100, then press continue.

At this point the tape is read. All points specified for all clocks

specified are read. For 8 clocks and 100 points this may take about 6

minutes. Then a branch to question 10, the actual processing, occurs.

16
10. "Compute sigma(y)?" If one wishes a sigma-tau plot of the data, the

answer to this question should be "y". If not the program branches to the

point where it asks whether a phase plot is desired. (Question 13).

11. "Subtract linear Lst sqr fit?" Mere, if one answers "y" , the

program will subtract the best linear least square fit from the data points

stored in the 9825A registers for that clock. The orginal data, for that

clock, as read from the tape is now modified by this procedure, and is lost.

If one wishes to reclaim the original data, the tape must be read again for

that clock. The least square fit data are retained in the registers for that

clock and are used for the sigma-tau plot and for the phase plot that may

follow. In the sigma(y) print out following a "y" answer to both 4. and 5.,

the intercept, Y, the fractional frequency, for the least square line, is also

printed out just before the sigma-tau values for the data set for that clock

and run.

12. "Plot sigma?" In this case a "y" answer will set up the plotter for

a sigma-tau plot. If a point plot is desired, the operator need only press

continue in response to the display:

"sig y plot: if line plot cfg6"

If a solid line plot is desired, one should type "cfg6", then press execute,

then continue. A pause and prompt to set paper in the plotter follows. Once

the paper is set, press continue and the plot will be completed.

13. "Plot Phase?" A "y" answer here will result in a phase plot with

either a least square fit subtracted, or not, as requested by the operator in

question 13. A prompt and pause to permit replacement of paper in the plotter

occurs. When paper is ready, press continue and the plot follows.

This is the last portion of the processing tor any clock. After this,

the program returns to the point, question 10, at which the data for the next

17
clock are processed. Questions 10 through 13 are again answered by the

operator. After data for all clocks specified have been processed, the

program ends, and displays:

"Stop. . .Operation complete".

6. Summary of Key Commands and Block Diagrams

A. Key commands used by the quad measurement modules (PDM) and by the

pulse distribution modules, (OMM)

1. Quad measurement module

A. Overall function codes

F8A15N3...Test LAM in first OMM.

Response goes to Q

F8A15N5...Test LAM second QMM

Response goes to Q

B. Section Function Codes

1. Section 1, A0 subadresses, use N3 for the

first QMM, and N5 for the second QMM

F0A0N3...Read 10Hz register

F9A0N3... Reset 10Hz register o'flow

F12A0N3... Reset 10 Hz register

F24A0N3. . .Disable channel operation

F27A0N3...Test if channel active,

Response goes to Q

2. Section 1, Al subaddresses, use N3 for the first QMM,

and N5 for the second QMM

F0A1N3... .Read 10MHz register

F10A1N3... Reset LAM status

F24A1N3... Disable channel LAM interrupt

F26A1N3... Enable channel LAM interrupt

F27A1N3. . .Test LAM status, response goes to Q

3. Section 2, use N3 for the first QMM, and N5 for the

second QMM

Use same commands as Section 1, but use subaddress:

A2 in place of A0

A3 in place of Al

4. Section 3, use N3 for the first QMM, and N5 for the

second QMM

Use same commands as Section 1, but use subaddress:

A4 in place of A0

A5 in place of Al

18
5. Section 4, use N3 for the first OHM,

and N5 for the second OMM

Use same commands as Section 1, but use subaddress

A6 in place of AO

A7 in place of Al

2. Pulse distribution module

A. Overall function codes (Subaddress AO)

F0A0N2...Read status

F8A0N2...Test LAM, Response goes to

F10A0M2. . .Reset LAM status and stop measurement cycle

F24A0N2... Disables PDM LAM interrupt

F25A0N2. . .Start next measurement cycle

F26A0N2... Enable PDM LAM interrupt

B. There are no other subaddresses used bv the PDM

B. Diagrams of operational modes

1. Fig. 1. 2. Fig. 2.

3. Fig. 3.

Control logic, Pulse Distribution Module,

Control logic, Quad Measurement Module.

Counting logic, Quad Measurement Module.

19
Footnotes:

(1) Supplied for this application by Kinetic Systems Corporation,

Lockport, 111

(2) Based on NBS-supplied conceptual specifications, ERBTEC Engineering

Inc., Boulder, CO., designed and manufactured the pulse distribution and quad

measurement modules used in this implementation. The original NBS specification and critical ANSI/ IEEE-583 interface requirements for these two module

types are contained in Section 6. More detailed CAMAC ANSI/ IEEE instrumentation standards may be found in (4).

(3) These items were supplied by Hewlett-Packard Co., Denver, Co.

(4) CAMAC Instrumentation and Interface Standards, Institute of

Electrical and Electronics Engineering, Inc., 345 E. 47th St., New York, NY

10017.

DISCLAIMER

Certain commercial equipment, instruments, or materials are identified in this document in order

to adequately specify the experimental procedure.

Such identification does not imply recommendation

or endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment

identified are necessarily the best available for

the purpose.

20
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23
APPENDIX

36th Annual Frequency Control Symposium - 1982

PERFORMANCE OF AN AUTOMATED HIGH ACCURACY

PHASE MEASUREMENT SYSTEM

S. Stein, D. Glaze, J. Levine, J. Gray, D. Hi 11 iard, D. Howe Time and Frequency Division

National Bureau of Standards

Boulder, Colorado 80303

and

L. Erb

ERBTEC Engineering Inc. Boulder, Colorado

Summary

A fully automated measurement system has

been developed that combines many properties

previously realized with separate techniques.

This system is an extension of the dual mixer

time difference technique, and maintains its

important features: zero dead time, absolute

phase difference measurement, very high precision, the ability to measure oscillators of

equal frequency and the ability to make mea,sure- ments at the time of the operator's choice. For

one set of design parameters, the theoretical

resolution is 0.2 ps, the measurement noise is 2 ps rms and measurements may be made within 0.1 s of any selected time. The dual mixer technique

has been extended by adding scalers which remove

the cycle ambiguity experienced in previous

realizations. In this respect, the system

functions like a divider plus clock, storing the

epoch of each device under test in hardware.

The automation is based on

2 the ANSI/IEEE583 (CAMAC) interface standard. Each measurement channel consists of a mixer, zero-crossing

detector, scaler and time interval counter. Four channels fit in a double width CAMAC module

which in turn is installed in a standard CAMAC

crate. Controllers are available to interface

with a wide variety of computers as well as any IEEE-488 compatible device. Two systems have

been in operation for several months. One operates 24 hours a day, taking data from 15 clocks for the NBS time scale, and the other is used for short duration laboratory experiments.

Review of the Dual Mixer

Time Difference Technique

It is advantageous to measure time directly

rather than time fluctuations, frequency or frequency fluctuationns. These measurements

constitute a hierarchy in which the subsequently

listed quantities may always be calculated from

the previous ones. However, the reverse is not true when there are gaps in the measurements.

In the past, frequency was usually not derived

from time measurements for short sample times

because time interval measurements could not be performed with adequate precision. The dual

mixer technique, illustrated in Figure 1, made

it possible to realize the precision of the beat

frequency technique in time interval measurements.

The signals from two oscillators (clocks) are applied to two ports of a pair of double balanced mixers. Another signal synthesized from one

of the oscillators is applied to the remaining

two ports of the mixer pair. The input signals

may be represented in the usual fashion

V

x

(t) =V

1Q

sin [2;n> 10

t + f^t)],

V

2 (t) = V2Q

sin [2m>

20

t + ^(t)] and

V

s (t) = V

so cos[2nvso

t +

4

s (t)]

where v = v,q(1-1/R) and R is a constant usually called the heterodyne factor.

The low passed outputs of the two mixers

are

V B1 = V B10

sin [ *l (t) "*s(t)] and

VB2

= VB20

sin t*2 (t) "*s

(t)] where

*(t) = 2m>

o

t + <t>(t).

The time interval counter starts at time tM when

Vn-> crosses zero in the positive direction and

stops at time t

N

, the time of the very next positive zero crossing of Vno- Thus

*1( V " W= 2Mn and

*

2 (t

N

) - *

s (t

N

) = 2Nn where

N and M are integers.

Subtracting the two equations in order to com- pare the phases of oscillators 1 and 2, one obtains

*

2 (t

N )-*1

(tM

) = *

s (t

N )-*

s (tM

)+2(N-M)7t.

The phase of an oscillator at time t>, may

be written in terms of its phase at tM and its

24
average frequency over the interval t,. < t*,.

(tii) = (tM ) + 27i[v(tM

;tN )](tN -tM ) and

"N

J L M M

,U

N

; "N "M J

when we apply this equation to both *

2 and 4> s we find

W'W = 2(N_M)n

-2n[v

B2

(tM;tN )](t

N -tM

)

where v g2 = v ?" v

s' Since M and N are not measureable with the equipment in Figure 1, the dual mixer technique

has heretofore only been used to measure the

phase difference between two oscillators modulo

2n. We denote the period of the time interval counter time base by t and the number of counts recorded in a measurement by P. Then the phase

difference between the two oscillators is given

by

[2 (t

M )-*1 (tM )]mod 2ti = -27i[v B2

(tM;t

N )]x

c

P

Figure 2 illustrates the output of the measurement system over a period of time. If a measurement begins and ends without the time

interval counter making a transition between

zero and its maximum value, e.g., t < t„ < t

N

<

t. , then the phase difference can Be calculated

from the data. If t < tM

< t. < t

N

< t , then

the data must be correctea by 2n t!o calculate

the phase difference. Experience has shown that

there are many measurement situations for which

the number of transitions of the time interval counter which occur between tw

and t

N cannot be

known. For this reason, a modification has been

developed which removes the ambiguity by measuring M and N.

Extended Dual Mixer Time

Difference Measurement Technique

In order to configure the system to acquire

complete phase information, two scalers are added to count the zero crossings of each mixer.

Figure 3 is the block diagram of a two channel

system. It is constructed from identical circuit modules and therefore contains an unused

time interval counter. However, this design

permits very straightforward, and inexpensive

extension to the comparison of an arbitrarily

large number of oscillators with no need for

switching any signals.

The counter outputs are combined to form

the phase difference between oscillators.

2 (tM

)-*

1 (tM

) = 2(N -M

o

)tt + 2(N-M)n

-27t[u B2

(t

M

;t

N )]t

c

P

The first term is a constant which represents

the choice of the time origin and can be ig- nored. The last two terms and their sum are plotted in Figure 4.

The average l^eat Frequency uTM UM

;t N

) cannot be known exactly. However, ft may Be estimated with sufficient precision from the

previous pair of measurements designated ' and

. The average frequency is approximately

v

B2

(tM;tN

) = (N"-N l )/[R(M"-M')/v

10

+ x c

(P' •P')]

provided that it changes sufficiently slowly

A typica

in the following

compared to the interval tM<tk] . A typical value

for this

section. error will be g^vef

Hardware Implementation

All measurement channels consist of a mixer, zero-crossing detector, scaler and time

interval counter. Four such circuits can be built in a double width CAMAC module. The

system is easily expanded to compare many oscillators and a complete system for making phase

comparisons among four clocks is shown in Figure

5. -We have chosen parameters which are reason- able for comparing state-of-the-art atomic standards. Thus, the synthesizer is offset 10Hz

below oscillator # 1 and R = 5 x 10 . The

outputs from both mixers are approximately 10Hz. The noise bandwidth is 100 Hz. The time interval counter is twice the frequency of oscillator

#1 or approximately 10 MHz. The quantization

error is 1/2R =10 cycle or 0.2ps which is a factor of ten smaller than the measurement

noise. As stated earlier, an error will result

from frequency changes which violate the con- stancy assumption .used to estimate v

R? . A change in v„ by 10 during the interval be- tween two measurements will result in a time

deviation error of lOps. Thus, one must make more closely spaced measurements for oscillators

which have large dynamic frequency changes than

for more stable devices. Two other sources of

inaccuracy are the sensitivities to the amplitude and phase of the common oscillator. Figure

6 shows the measured value of x = 4>/2n\> as a function of the amplitude of the input signal

and the phase of the synthesizer.

The new measurement system has many desirable features and properties:

(1) It has very high resolution, limited by the

internal counters to 0.2 ps and by noise to approximately 2 ps.

(2) It has much lower noise than divider based measurement systems. However compromises

made to achieve low cost, low power, small size and automatic operation degrade the

performance compared to state-of-the-art

systems for comparing 2 oscillators.

(3) The operation is fully automatic.

(4) NBS has developed a detailed operating

manual for the equipment and software.

25
(5) All oscillators in the range of 5 MHz + 5 Hz may be compared. Other carrier frequencies such as 1 MHz, 5.115 MHz, 10 MHz and

10.23 MHz are also usable. However, different carrier frequencies may not be mixed

on the same system. The system has been

successfully tested with an oscillator off- set 4.6 Hz from nominal 5MHz. Measurements

were made at intervals of 2 hours between

which the system had to accumulate approx- imately 2 x 10 n. The system has also been

tested with an oscillator offset 4 x 10 , and no errors were detected during a period

of 40 days.

(6) All sampling times in the range of 1 second

to 16 days with a resolution of 0.1 second

are possible. Measurements may be made on command or in a preprogrammed sequence.

(7) Measurements are synchronized precisely,

i.e. at the picosecond level, with the

reference clock. They may therefore be

synchronized with important user system

events, such as the switching times of a FSK or PSK system.

(8) All oscillators are compared synchronously

and all measurements are performed within a maximum interval of 0.1 second. As a re- sult, the phase of any oscillator needs to be interpolated to the chosen measurement

time for an interval of 0.1 second maximum.

This capability, which is not present in either single heterodyne measurement sy- stems or switched measurement systems

eliminates a source of "measurement" error which is generally much larger than the

noise induced errors. For example, interpolation of the phase gf a high performance

Cs clock (a " 10 A"5

) over a period of 3 hours woula produce approximately 1.5 ns phase uncertainty. To maintain 4 ps accuracy requires measurements simultaneous to

0.1s.

(9) There are no phase errors due to the switching of rf signals since there is no switching anywhere in the analog measure- ment system.

(10) No appreciable phase errors are introduced

when it is necessary to change the reference clock since, as shown in Figure 6, the

peak error due to changes in synthesizer

phase is 20 ps.

(11) The measurement system is capable of mea- suring its own phase noise when the same

signal is applied to two input ports.

Figure 7 shows the phase deviations between

two such channels over a period of 75,000

seconds and Figure 8 is the corresponding

Allan variance plot. Figure 9 shows the

phase deviations between 2 input channels

over a period of 40 days.

(12) Since the IEEE-583 (CAMAC) interface stan- dard has been followed for all the custom

hardware, the system may be easily interfaced to almost any instrument controller. NBS has already tested the system using a large minicomputer, a small minicomputer

and a desk top calculator. Interfaces

between IEEE-583 and IEEE-488 controllers

are available and have been used successfully.

(13) The system is capable of camparing a very

large number of oscillators at a reasonable cost per device.

There are also disadvantages to this mea- surement system. The most important are:

(1) The complexity of the hardware is greater

than for some systems. It is possible

that this will reduce reliability.

(2) A high level of redundancy is difficult to achieve. The system design stresses size, power, convenience and cost, resulting in an increase in the number of possible

single point failure mechanisms compared to some other techniques. For example, a CAMAC power supply failure will result in a loss of data for all devices being measured.

(3) A substantial committment is required in

both specialized hardware and software.

(4) If an oscillator under test experiences a phase jump which exceeds 1 cycle, the measurement system records a jump with

incorrect absolute magnitude. As a result,

it may not be applicable to signals which

are frequency modulated with discontinuous

phase steps larger than In.

Conclusions

We have demonstrated a new phase measure- ment system with very desirable properties: All oscillators in the range of 5MHz ± 5Hz may be

measured directly. The sampling times are only

restricted by the requirement that they exceed

one,,second. The noise floor is a (2,t) = 3 x 10 A in short term and the time deviations

are less than 100 ps. All circuitry is designed

as modules which allows expansion at modest

cost. Compatibility with a variety of computers

is insured through the use of the IEEE-583

interface and adapters are available to permit

use with an IEEE-488 controller. The system

makes it feasible to make completely automated

phase measurements at predetermined times on large numbers of atomic clocks. It's own noise

is one-hundred times less than the state-of-theart in clock performance. It will be used in the near future to make all measurement needed

to compute NBS atomic time, but it will also be very valuable for any laboratory which uses three or more atomic clocks.

References

1. D. W. Allan, "The measurement of frequency

26
2.

3.

and frequency stability of precision

oscillators," NBS Tech. Note 669

(1975). "CAMAC Instrumentation and Interface stan- dards," Institute of Electrical and Electronic Engineers, Inc., 345 E. 47th St. New York, NY 10017.

D. J. Glaze and S. R. Stein, "Picosecond

time difference measurements utilizing CA- MAC based ANSI/IEEE -488 data acquisition

hardware", NBS Tech Note 1056 (in preparation). V

B2 = V2 " V8

ZERO

CROSSING

DETECTOR

STOP

8TART

D

TIME INTERVAL COUNTER %

"«-

ZERO

CROSSING

DETECTOR

"»

[2

(tH

)-»

1 (tM

))»od 2n = -2n[J

B2

(tM

;tN)]t c

f>

Figure 1. Dual Mixer Time Difference Measurement System

Figure 2. Dual Mixer Data

+2 ©

FREQUENCY

SYNTH.

*1

0-

B2 r2

KS

ZERO

CROSSING

DETECTOR

SCALER

STOP

START

V

s = ^(1-1/R)

TIME INTERVAL COUNTER ^P

\

JH

ZERO

CROSSING

DETECTOR

-»

SCALER

STOP

START

"bi = VR

TIME INTERVAL COUNTER

Figure 3. Extended Dual Mixer Time Difference Measurement

System

27
W'W = 2(N

o" Mo

) " * 2(N" M)"

- 2n ^B2(t«

:tN

)1,

c P

-2"I»B2 (tM

:t

ll )lx

e

P

2(N-H)it Sum

Figure 4. Extended Dual Mixer Data

Clock *1 0—*—[>-

Synthesizer

">

• 0—0-1

Clock +4 [>

Offset 5 MHz

Start

PULSE DISTRIBUTION

MODULE

"rr-rr tt—n—rr

Start Start 10 MHz Time Base

Output ,nPut MEASUREMENT MODULE

Stop Inputs DATA

6X4= 24 clocks maximum

requires one pulse distribution module and

six measurement modules maximum

Figure 5. System Block Diagram

x(ps)

1000 -

800

600

i

1 400

200 e

e

a _!__

INPUT AMPLITUDE OdB «1Vrms

' I

I II -3 -6 -9dB

SYNTHESIZER PHASE

Figure 6. Measured Time Difference vs. Input Amplitude and

Synthesizer Phase

23
PHASE PLOT Cloak No. 4- B Lot Bar- Slope of - 1. 05B2OBo-l 7/6 R. nbo4o —nbo4b

>d E>W BS may B2

lo-ll

.Bo..«a

-lo-U 1

T- 747BB SECONDS

Figure 7. Raw Phase Data for Two Channels Driven from the Same Source

-12.

log Sidy

\ "" ' Mi IBflrls. Clook No, 4- 6

-14.

-is,

-i«

-17,

n >» in

log T

e

Figure 8. Noise Floor of Measurement System

29
e.ee 9.7S 19.se

I'fiYS 29.2' CLOCKS 11 )- 21 ) ,X0P6. •45647. 19-HOR-82

Figure 9. Raw Phase Data for Two Channels Driven from the Same Source

30
NBS-1 14A (REV. 2-80) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBS TN-1056

2. Performing Organ. Report No. 3. Publication Date August 1983

4. TITLE AND SUBTITLE

PICOSECOND TIME DIFFERENCE MEASUREMENTS UTILIZING CAMAC-BASED ANSI/IEEE-488

DATA ACQUISITION HARDWARE

OPERATION MANUAL IE3 Version 1.0

5. AUTHOR(S)

D. J. Glaze and S. R. Stein

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

10. SUPPLEMENTARY NOTES

2] Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) Automated time-difference measurements at the picosecond level have been

achieved. The system described combines the best properties of three common methods: the single heterodyne measurement technique, the frequency divider,

and the dual-mixer time-difference measurement system. This particular system

combines two instrumentation standards, ANSI/I EEE-583 and ANSI/IEEE-488 with

new, modular dual-mixer time-difference measurement hardware. The modular,

standardized hardware together with the new measurement techniques permit the

data acquisition modules to be contained in a standard CAMAC crate. This system,

along with an external controller, is capable of measuring eight clocks, at the

present time, and is expandable to twenty-four clocks with modified software and

additional measurement modules. The system noise performance is described by

-12 -1 a (t) = 3 x 10 t~ for time difference measurements.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

ANSI/IEEE-488; ANSI/IEEE-583; automated data acquisition system; dual-mixer

measurements; picosecond time-difference measurements.

13. AVAILABILITY

FJX) Unlimited

1 | For Official Distribution. Do Not Release to NTIS

|~~Xl Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

2] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

36

15. Price$3.75

JSCOMM-DC 6043-P80

<r U.S. Government Printing Office 1983 - 681-125/468 Reg.

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